Photographic reducing composition and process



Patented Jan. 18, 1944 Y PHOTOGRAPHIC REDUCING COMPOSITION AND PROCESS John Ran Weber, South River, N. 1., and Lynn Barratt Morris, Washington, D. 0.. ass'ignors,

by mesne assignments, to E.

L du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application September Serial No. 412,340

21 Claims.

This invention relates to photographic compositions and more particularly to photographic processing solutions and to photographic processes for utilizing such compositions. In One of its more specific aspects it relates to photographic reducing solutions for treating silver salts and photographic processe utilizing such solutions. In some of its further aspects it relates to new chemical compositions for photographic development and toning.

This invention has for an object to provide new and useful reducing compositions for silver salts. A further object is to provide a reducing agent which can be used for the reduction of photographic images in alkaline, neutral or acid media. A still further object is to provide more eflective and more economical reducing agents which can be used in acid media. A still further object is to provide new and useful developer solutions. Another object is to provide developer solutions for reversal processes. Yet another object is to provide a practical and economical means for toning a silver image to produce warm and pleasing brown to sepia toned images. Still other objects will be apparent from the following description of the invention.

It has been found that the oxygenated reaction products of hydrogen peroxide with thiourea and certain of its hydrocarbon substitution products have considerable utility in photographic processing baths especially for reducing silver salts to metallic silver in photographic elements.

The exact structure of oxygenated reaction products of thiourea with hydrogen peroxide prepared from these reactants in neutral solution is not known with certainty. It has been called thiourea dioxide by some investigators which is indicative of a formula such as that set forth in (A) below. Others, however, have advanced the name imino-amino-methane-sulfinic acid and formamidine sulfinic acid which implies a structure having formula (B) 1' It is possible that both formulae may be equally forms set forth above, which may undergo rearrangement depending upon whether the compound is in acid or alkaline medium, or upon physical characteristics such as temperature and pressure.

7 Furthermore, it is conceivable, considering the second formula, that it forms a salt when in alkaline solution e. g. the sodium sulfinate when in sodium hydroxide solution. It is further conceivable that in acid solution it forms salts on the imino group, for instance, a hydrochloride.

Since the utility of the compound in accordance with this invention does not depend upon the exact structure of thefoxygenated reaction product of thiourea or-hydrocarbon substituted thiourea with hydrogen peroxide, andfor convenience, the names imino-amino-methane sulfinic acid or formamidine sulfinic acid will be used. The expression an imino-amino-methane sulfinic acid will be used to cover formamidine sulfinic acid and its derivatives which are capable of reducing silver salts.

To be more specific, it has been found that an imino-amino-methane sulfinic acid in aqueous solution and especiall formamidine sulfinic acid is capable of preferential reduction of exposed silver halide grains in the presence of unexposed silver halides to give a photographic image so long as the solution is definitely acid. However, if the pH of the solution is increased toward neutral, the reduction potential of the compound increases, tending to give an overall blackening effeet which is relatively weak at a pH of 6 but quite powerful at pH values in excess of 6.8.

The last mentioned effect is advantageously used in accordance with one aspect of the invention in reversal processes. The ordinary processes of preparing positive images by removal of a negative image, followed by reduction ofthe remaining silver halides in a reducing solution containing an imino-amino-methane sulfinic acid, can be carried out with or without a second exposure to light. The most convenient method employ no second exposure, but merely consist of immersing the film, after the original image has been removed and the emulsion cleared and washed; in a. solu on containing sumcient formamidine sulfinic acid to reduce the silver salts to metallic silver. While acid solutions are useful, especially if re-exposure is resorted to, it has been found that alkaline solutions of an imino-amino-methane sulfinic acid have a power ful reducing action on exposed or unexposed sllve halide grains. This is especially true of formam idine sulfinic acid.

In a further aspect of the invention an iminoamino-methane sulfinic acid is used in acid solution as the ordinary developer. Such solutions are capable of reducing the silver halide grains of an exposed photographic emulsion to form a metallic silver image. A silver halide emulsion containing latent images as formed by exposure to an original scene or by printing from a developed photographic element, is treated in an aqueous acid solution containing sufllcient of an imino-amino-methane sulflnic acid to develop the exposed silver salts. Formamidine sulflnic acid developers, however, are preferred.

In still another aspect of the invention, aqueous acidic solutions containing small amounts of an imino-amino-methane sulflnic acid are used to redevelop a bleached silver image. A photographic element containing a bleached silver image is immersed in an aqueous acidic solution of the type described in sumcient amount to reduce the silver salts. The resulting image is characterized by various tones depending upon the particular pH value of the developer formula.

The treating solutions used in the processes outlined above may contain in addition to the imino-amino-methane sulfinic acid various modifying agents which are useful in developer solutions such as restrainers, preservatives, agents for controlling image tone, wetting agents, hardeners, materials whose presence retards the rate of diffusion of the solution in emulsion layers etc. The invention, however, is not limited to solutions, on the contrary, dry reducing compositions containing the specified ingredients with the exception of water are comprehended.

The invention will be further illustrated, but is not intended to be limited by the following examples. The first group consists of developer solutions useful for ordinary development of silver images or sepia toning by redevelopment. They can be made by admixing the ingredients in any desired order with water. Dry compositions can be made in a similar manner by admixing the components in dry forms.

ExAMPLE I Formamidine sulfinic acid grams 18 Sodium bisulflte do. 36 Potassium bromide do 6 Water millilii-pr 100 ExAuPL II Formamidine sulflnic acid grams 15 Sodium bisulflte do 20 Potassium bromide do Potassium metabisulflte do 6 Water milliliters 1000 EXAMPLE III Formamidine sulfinic acid "grams" 24 Sodium bisulflte do.. 52 Potassium bromide do 8 Water mil1iliters 1000 I ExAmPLE IV Formamidine sulflnic acid grarns 20 Sodium bisulflte do 45 Potassium bromide do 5 Water -inilliliters 1000 ExAuPLE V Formamidine sulflnic acid grams Potassium bromide do 3 Potassium metabisulfltedo 9 Water 1 ers-.. 1000 EXAMPLE VI Formamidine sulfinic acid "grams" 4.5 Potassium bromide do 3 Potassium metabisulfite do 45 Water "milliliters" 1000 EXAMPLE VII Formamidine sulflnic acid "grams..- Potassium sulfite ..do Potassium bromide do 30 Sodium hydroxide do 20 Water milliliters 1000 EXAMPLE VIII Formamidine sulfinic acid grams 5 Hydroquinone do 10 Potassium carbonate do 30 Potassium su1flte -do Water milliliters 1000 EXAMPLE IX EXAMPLE X Formamidine sulfinic acid grams Sodium carbonate ..do Sodium sulfite do Water milliliters EXAMPLE XI Formamidine sulfinic acid grams 8 Potassium br do 15 Sodium hydroxide do 15 Water miililiters 1000 The amount of formamidine sulflnic acid is not limited to that set forth in the above examples but may be varied over a, wide range. The amount to be used varies somewhat in accordance with the material treated.

Acid development In the acid reduction or development procedures a range of concentrations from about 0.5% to 2.0% by weight of formamidine suliinic acid in respect to the final weight of the solution represents a practical range. N-hydroearbon substituted formamidine sulflnic acids can be used in like amounts.

The compositions of the acid baths should be balanced so that the pH value of the developing bath is from pH 3 to pH 6. Values higher or lower than those given will usually produce poor results, a higher pH tending to produce a fog and too low a pH slowing down the reducing action to an unworkable extent. By proper adjustment both negative and positive plates, films and papers can be satisfactorily developed. The pH concentrations can be adjusted by the addition of various acidic or alkaline materials or compounds such as lactic acid, glycollic acid, sodium acetate, sodium amino acetate, sodium citrate, boric acid, etc.

Toning development Redevelopment of a bleached silver image as above described in an imino-amino-sulflnic acid developer of the acidic type especially aqueous formamidine sulfinic acid developers, has a surprising and unexpected effect on the color of the image produced. Instead of the normal image tones obtained by the development of an original exposed but undeveloped emulsion, the bleached image reappears in brownish to sepia tone values. Any one of the common bleaching baths known to the art may be used, such as ferricyanidebromide or copper sulfate chloride bleaches. A developed film, plate or paper print which has been fixed and thoroughly washed is simply immersed in a bleaching bath until the image is thoroughly bleached and is then washed and transferred to a bath containing a developing bath of formamidine sulfinic acid. After a short time the image reappears in brownish to sepia tones which may be varied by changes in the developing bath. A more convenient method of varying the tone values, however, can be used in which the original image is first bleached, then washed, then developed in a dilute metolhydroquinone developer, neutralized in an acid stop bath after partial redevelopment and then transferred to a formamidine sulfinic acid developer to complete the redeveloper. The first part of the development in an ordinary alkaline developing bath converts parts of the latent image to metallic silver and the rest is converted to brown silver salt by the formamidine sulfinic acid bath. By varying the length of time the emulsion is in each bath, many different intermediate tones between brown and black may be produced. The amount of imino-aminomethane sulfinic acid has some effect on the image color. In general, the higher the concentration the darker the image. Amounts from 0.5% to 2.0% by weight of the sulfinic acidin respect to the final weight of the solution gives satisfactory results. However, lesser amounts and amounts in excess of 2.0% may be used.

Various other developing agents can be used in place of the metol-hydroquinone developer. Suitable agents include chlorohydroquinone, 2:4-diaminophenol hydrochloride and p-hydroxyphenyl amino acetic acid.

Reversal development Various procedures can be used in this phase of the invention. In general, however, an exposed film, plate or paper'print is developed according to the usual procedure known to the art and then bleached in an acid solution of potas sium bichromate which removes the silver image. After washing and clearing in a sodium bisulfite solution, the photographic element is then transferred to an alkaline solution of formamidine sulfinic acid such as those described in Examples I and VI. This bath rapidly reduces all the silver halide which was not originally affected by the light and bleached out after development. Consequently a reversed image is produced which may be fixed, hardened and Washed to give a positive image of the original subject. An alkaline formamidine sulfinic acid solution to be used in such a process should preferably contain from about 0.5% to 3% by weight of formamidine sulfinic acid. For best results the pH of such solution should be above 9.5.

Other N-hydrocarbon substituted imino-amino-methane sulfinic acids which are capable of reducing silver salts, can be used in the above described procedures and compositions in similar amounts. Suitable substituents include lower alkyl groups, e. g. methyl and ethyl; aryl radicals,

e. g. phenyl, chlorphenyl, etc. Suitable substituted compounds include N-methyl formamidine sulfinic acid, N-ethyl formamidine sulfinic acid, N-alkyl formamidine sulfinic acid, N-phenyl formamidine sulfinic 'acidand N-chlorophenyl monium and amine salts of sulfurous acid, e. g.

triethanolamine-, morpholine-, tetramethylammonium-, and trimethylbenzylammonium sulfit'es. A portion of the bisulfltes can be replaced by lithium sodium, potassium and ammonium bisulfites and meta bisulfites. Other compounds include acetone bisuifltes, formaldehyde sodium sulfoxylate, hexahydric alcohols and lactic and glycollic acids.

Similarly in place of the specific restrainers of the above examples which can be interchanged in any desired manner, can be substituted one or more other compounds of this type. Suitable other compounds include, sodium and lithium bromides, chlorides. and iodides potassium chloride and iodide, ammonium bromide, etc.

Agents for controlling the image tones can be incorporated with the novel reducing 'agents hereof. Among the useful agents are quinone hydrochloride, quinoline, 5-nitrobenziminazole, triazole, benztriazole, iminazole, pseudo thiohydantoin, indophenyl iodonium chloride, etc.

Compounds which retard the rate of diffusion of solutions through emulsion layers, e. g. sugar, etc., may be added to the reducing compositions. Similarly wetting agents such as the sodium salts of alkyl sulfates and alkyl sulfonic acids of 8 to 18 carbon atoms; C- and N- alkyl betaines wherein the alkyl groups contain 8 to 18 carbon atoms, etc. can be used in the compositions and procedures. Also emulsion hardeners such as potassium aluminum sulfate and chrome alum have a useful hardening action in solutions of low pH. Aldehyde hardeners are useful in alkaline or neutral solution.

The developer or reducing solutions of this invention are useful in developing various types of photographic elements such as camera, cinema, portrait, lithographic and X-ray, films and plates and photographic papers, etc. They are useful with various types of film base materials and do not have a deleterious effect thereon. Thus cellulose derivative film bases, e. g. cellulose nitrate, methyl cellulose, ethyl cellulose acetate, cellulose acetate-propionate and" cellulose ester and ether film bases, in general; synthetic resins, e. g. polyvinyl acetals, etc.; and super polymers, e. g. nylon, may form part of the elements treated. 1

Various types of silver halide emulsion layers may be treated as will be apparent from the above. For instance, simple and mixed silver chloride, silver bromide, silver iodide, silver chloride-bromide. and silver chloi'ide-bromide-iodide, gelatin emulsion layers, may be satisfactorily processed by the novel solutions and procedures hereof.

The reducing solutions can be used with various types of colloid binding media. They do not have harmful effects on gelatin, agar agar, albumins, synthetic resins, e. g. polyvinyl acetals sulfoxylates.

used as the binding agents for the silver salts.

The baths can be used over a fairly wide range temperature with complete safety. In addition, they have a fairly long useful life throughout practical processing temperatures. One of the most important advantages of the invention is that iormamidine sulfinic acid is a much more energetic photographic reducing agent in both acid and alkaline solutions than are the compounds already employed in the art. Overall blackening by alkaline solutions in reversal processes is likewise more easily and quick- 1y obtained by the compound of the invention than by equivalent quantities or hydrosulfltes or Another advantage of the invention is that it permits the formation of brownish to sepia tonedimages having wide gradation of color from reddish brown to brownish black by partial redevelopment of a bleached silver image in an ordinary developer and completing the redevelopment in a formamidine sulfinic acid developer.

As many apparently widely difierent embodiments of this invention may be made, without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments hereof except as defined by the appended claims.

We claim:

l. A photographic reducing solution containing a water soluble sulfite and an imino-aminomethane-sulfinic acid.

2. A dry photographic reducing composition containing a water soluble sulfite and an iminoamino-methane-sulfinic acid.

3. Min aqueous acidic photographic reducing solution containing a water soluble sulfite and an imino-amino-methane-sulfinic acid.

4. An alkaline photographic reducing composition containing an alkaline compound, a water soluble sulfite and an imino-amino-methane-sulfinic acid. t,

5. A dry photographic reducing composition containing an alkaline compound, a water soluble sulfite and an imino-amino-methane-sulfinic acid.

6. An aqueous photographic reducing solution containing a water soluble sulfite and formamidine sulfinic acid.

7. An aqueous acidic photographic reducing solution containing a water soluble sulfite and formamidine sulfinic acid.

8. An alkaline photographic reducing solution containing an alkaline compound, a water soluble sulfite and formamidine sulfinic acid.

9. The process which comprises reducing a light sensitive photographic element in an aqueous solution containing an imino-amino-meth ane-sulfinic acid.

10. The process which comprises developing a photographic element containing a silver salt layer in an aqueous solution containing formamidine sulfinic acid.

11. In a photographic reversal process involving a first development and bleaching of developed images, the step which comprises developing the reversed image in an aqueous solution containing an iminoamino-methane-sulfinic acid. a

12. A photographic process for obtaining direct positives which comprises efiecting a first development, removing the silver image formed and effecting a final reduction of the remaining silver salt in an aqueous solution containing an iminoamino-methane-sulfinic acid.

13. A photographic process for obtaining direct positives which comprises effecting a first development, removing the silver image formed and effecting a final reduction of the remaining silver salt in an aqueous solution containing formamidine sulfinic acid,

14. A photographic process for obtaining direct positives which comprises effecting a first development, removing the silver image formed and effecting a final reductilon of the remaining formsalt in an alkaline solution containing formamidine sulfinic acid.

15. A photographic process for obtaining direct positives which comprises effecting a first development, removing the silver image formed and effecting a final reduction of the remaining silver salt in an alkaline solution containing an iminoamino-methane sulfinic acid.

16. A photographic process for obtaining direct positives which comprises effecting a first development, removing the silver image formed and effecting a final reduction of the remaining silver salt in an alkaline solution containing formamidine sulfinic acid having a pH in excess of 6.8.

17. The process of producing reddish brown to sepia tones in a photographic silver image which comprises redeveloping a bleached silver image in an aqueous solution containing an iminoamino-methane-sulfinic acid .having a pH less than 6.0.

18. The process of producing reddish brown to sepia tones in a photographic silver image which comprises redeveloping a bleached silver salt image in an aqueous solution containing formamidine sulfinic acid having a pH less than 6.

19. The process of toning which comprises partially developing a bleached image with an ordinary developing agent and completing the development in an aqueous solution containing an imino-amino-methane-sulfinic acid.

20. An alkaline photographic reducing composition containing an alkaline compound, a water soluble sulfite, and formamidine sulfinic acid.

21. An alkaline photographic reducing composition containing sodium hydroxide, an alkali metal sulfite and formamidine sulfinic acid.

JOHN RAU WEBER. LYNN BARRA'I'I' MORRIS. 

